"I have no doubt that these islands will be inundated," says MacKenzie, "or if they're not inundated, that the livelihood of people will be very difficult, because [climate change] will affect saltwater incursion into our water tables, it will affect our plant life, and it will affect the water we drink."

MacKenzie gazes off to the right toward the curving line of coconut palms spanning the 40-mile coast of the lagoon before him. Beads of sweat cross his brow, and he raises a hand to shield his eyes from the sun.

"It's interesting," he says. "People on the islands have begun to measure erosion according to how many rows of coconut trees have died back. There used to be three rows of trees here" -- he points to the open, sandy beach -- "but now they are gone."